Owing to their unique physicochemical properties, MXenes have emerged as promising materials for biosensing applications. This review paper comprehensively explores the recent advancements in MXene-based biosensors for health and environmental applications. This review begins with an introduction to MXenes and biosensors, outlining various types of biosensors including electrochemical, enzymatic, optical, and fluorescent-based systems. The synthesis methods and characteristics of MXenes are thoroughly discussed, highlighting the importance of these processes in tailoring MXenes for specific biosensing applications. Particular attention is given to the development of electrochemical MXene-based biosensors, which have shown remarkable sensitivity and selectivity in detecting various analytes. This review then delves into enzymatic MXene-based biosensors, exploring how the integration of MXenes with enzymes enhances sensor performance and expands the range of detectable biomarkers. Optical biosensors based on MXenes are examined, focusing on their mechanisms and applications in both healthcare and environmental monitoring. The potential of fluorescent-based MXene biosensors is also investigated, showcasing their utility in imaging and sensing applications. In addition, MXene-based potential wearable biosensors have been discussed along with the role of MXenes in volatile organic compound (VOC) detection for environmental applications. Finally, this paper concludes with a critical analysis of the current state of MXene-based biosensors and provides insights into future perspectives and challenges in this rapidly evolving field.

The impact of a CeO₂-ZnO nanocomposite on the photocatalytic and antibacterial properties compared to bare ZnO was investigated. A CeO₂-ZnO nanocomposite was synthesized using Acacia nilotica fruit extract as a novel fuel by a simple solution combustion method. The obtained CeO₂-ZnO nanocomposite was confirmed structurally by XRD, FTIR, Raman and UV-DRS and morphologically by SEM/TEM analysis. The XRD pattern indicates the presence of both hexagonal Wurtzite-structured ZnO (major) and cubic-phase CeO₂ (minor). FTIR shows the presence of a Ce-O-Ce vibration at 468 cm⁻¹ and Zn-O vibration at 445 cm⁻¹. The existence of a band at 460 cm⁻¹ confirmed the F_2g Raman-active mode of the fluorite cubic crystalline structure for CeO₂. Diffused reflectance spectroscopy was used to estimate the bandgap (E_g) from Kubelka–Munk (K–M) theory which was found to be 3.4 eV. TEM analysis shows almost spherical-shaped particles, at a size of about 10–15 nm. The CeO₂-ZnO nanocomposite shows a good BET specific surface area of 30 m²g⁻¹. The surface defects and porosity of the CeO₂-ZnO nanocomposite caused methylene blue (MB) dye to degrade under sunlight (88%) and UV light (92%). The CeO₂-ZnO nanocomposite also exhibited considerable antibacterial activity against a pathogenic bacterial strain.

Detection of the Cu²⁺ ions is crucial because of its environmental and biological implications. The fluorescent-based organic sensors are not suitable for Cu²⁺ detection due to their short penetration depth caused by the UV/visible excitation source. Therefore, we have demonstrated a highly sensitive and selective near-infrared (NIR) excitable poly(acrylic acid) (PAA) coated upconversion nanoparticles (UCNPs) based sensor for Cu²⁺ detection. We construct the PAA modified Na(Yb, Nd)F₄@Na(Yb, Gd)F₄:Tm@NaGdF₄ core-shell-shell structured UCNPs based sensor via a co-precipitation route. The upconversion emission intensity of the PAA-UCNPs decreases linearly with the increase in the Cu²⁺ concentration from 0.125 to 3.125 μM due to the copper carboxylate complex formation between Cu²⁺ and PAA-UCNPs. The calculated detection limit of the PAA-UCNPs based sensor is 0.1 μM. The PAA-UCNPs based sensor is very sensitive and selective toward detecting the Cu²⁺ ions, even when the Cu²⁺ co-exist with other metal ions. The EDTA addition has significantly reversed the upconversion emission quenching by forming the EDTA-Cu²⁺ complex based on their greater affinity toward the Cu²⁺. Therefore, the PAA-UCNPs based sensor can be a promising candidate for Cu²⁺ detection because of their higher sensitivity and selectivity under 980 nm NIR excitation.

KYb₂F₇:Er³⁺ UC nanocrystal-based nanothermometers have greatly improved the S_R with ion substitution of Ti⁴⁺, Ge⁴⁺, and Y³⁺ for Yb³⁺.